Live for ever … Jonny Greenwood (left) on stage with the London Contemporary Orchestra. Photograph: Atherton Chiellino

In a year off from Radiohead, I've been writing scored music for small string groups – first a residency with the Australian Chamber Orchestra (who really do practise all day and surf all evening) and, more recently, the London Contemporary Orchestra (LCO). It's intended for concerts instead of recordings, which is a new way of thinking about music for me. It's led me to think differently about live music. And while I regret that there's an exclusivity to working like that, I don't regret the time spent hearing orchestras and small string groups up close.

It's a very affecting thing to be in the same room as these musicians – a little embarrassing, even. You're being shown something so personal, especially with chamber music, that it's almost awkward. Listening to the ACO rehearse Shostakovich string quartets was the musical highlight of my trip to Australia, and watching the LCO play is a thrilling experience that recordings can't match.

I love the impermanence of the music live: it's played in the room – which is itself infinitely variable from one concert to another – and then it's gone, soaked into the walls. Unlike recordings, it isn't identical to the previous performance or the next one. It can go slightly (or badly) wrong at any time. And all that is shared equally by everyone in the room.

I played one show with the LCO at the Wapping Project in London, and on Saturday 14 June we're playing at the wind tunnels in Farnborough, Hampshire – neither space is intended for concerts. The wind tunnels should be really interesting, but we won't really know until we start – which is kind of the point. All these variables add to the complexity and unpredictability of the sound.

I was raised on recordings and led to trust them as interchangeable tokens of the real thing, but there's something so strange about live classical music that over the years has made me lose this belief. A big part of this is the quality of the sound. I should know, because I had my embarrassing hi-fi phase in the 90s. It was like having a secret vice: the magazines, the specialist shops full of solitary, shuffling men – and all in the pursuit of a solitary domestic pleasure. What did it have to do with making music?

The first warning sign was the shop's demo CDs waiting on top of the £10,000 amp (and you really needed two of them – one for each speaker): lots of late Steely Dan (a PA tester's favourite, too) lots of Sting, some Kenny G and a token pile of Vivaldi's Four Seasons. These would have the all-important DDD marking – denoting fully digital recordings, from original session to mastering. That proved it: people into hi-fi had a worryingly clinical taste in music.

Or was it the other way round? Perhaps Kenny G fans just loved hunting for more and more sonic purity. More likely, the technology led the taste. Audiophile listeners start shedding dirtier favourites as soon as they start worrying about sound quality, replacing them with cleaner recordings and then cleaner music. Getting into late Steely Dan because of how it sounds, or just avoiding anything recorded more than 20 years ago. Shelving those Fall CDs for being "too hissy". Letting the speakers dictate what's played though them.

I went into one shop with Radiohead's producer Nigel Godrich. Seeing the prices, he asked the owner: "Why would you need to listen to OK Computer on a CD player that costs more than the tape machine which we recorded it on?"

"Ah," he replied. "You're one of these people who think digital is just ones and zeros."

Bands today try to replicate that recording in the belief that its rough sound can be emulated with a rough recording – one bad mic, and all in one room. That it can't be replicated only makes that album even more of an achievement for Chris Thomas and Bill Price, and the notion of what makes a good recording even harder to pin down. That's why I still enjoy recording studios and why I am so often seduced by electronic music, which stands above all this and thrives on the airlessness of its recordings.

And yet, applied to acoustic classical music, all bets are off. I don't trust microphones or speakers for that, whether it's recorded or played live. They approximate and inflate rather than distil and concentrate. And with sonically complex contemporary music such as Ligeti or Penderecki, mics and speakers make things sound harsh and discordant. The live experience is far softer, stranger and more colourful than two speakers can put across. If you haven't heard it live, you haven't really heard it – and yet 90% of judgments on classical music are made from hearing recordings.

When an orchestra starts from silence in a quiet room it's glorious. Or a solitary singer. It doesn't matter how much you spend on your speaker stands, you can't reproduce that in your front room, any more than the National Geographic channel reproduces Madagascar. It's all a con. If you're interested, hunt out live classical music, especially the kind that doesn't rely on PA systems. Think of those speakers as barriers instead of amplifiers, and listen to the real thing whenever you can.

• Jonny Greenwood performs with the London Contemporary Orchestra at the Farnborough wind tunnels on 14 June. Ticket information.